The 2021 FIA WRC3 Championship was the eighth season of WRC3, a rallying championship organised and governed by the Fédération Internationale de l'Automobile as the third-highest tier of international rallying. It was open to privately entered cars complying with Group Rally2 regulations. The championship began in January 2021 with the Rallye Monte-Carlo and concluded in November 2021 with Rally Monza, running in support of the 2021 World Rally Championship.

Yohan Rossel won the driver's championship, while Maciek Szczepaniak took the co-driver's title.

The 2020 WRC3 driver and co-driver champions Jari Huttunen and Mikko Lukka did not defend their titles in 2021 due to progression to WRC2. Frenchman Yohan Rossel took the driver's title at the final round but due to his employing multiple co-drivers through the season, the co-driver title went to Maciek Szczepaniak, regular co-driver to Kajetan Kajetanowicz.

The 2021 WRC3 season was the last to use Group Rally2 cars. From 2022 the championship would use only Group Rally3 cars.

The 2021 championship was contested over twelve rounds in Europe and Africa:

The following rounds were included on the original calendar published by WRC Promoter GmbH, but were later cancelled:

With the addition of Rally Chile to the calendar in 2019, the FIA opened the tender process for new events to join the championship in 2020. Three events were successful, but the championship was affected by a series of cancellations in 2019 and 2020 that necessitated changes to the 2021 calendar:

In light of the disruption caused by the pandemic in 2020 and in anticipation of further delays, the calendar included an additional six reserve rounds that could be included in the event of rallies being cancelled. These events include rallies in Turkey, Argentina and Latvia. The Ypres Rally had also been included on this reserve list before it replaced Rally GB, so as the Acropolis Rally and Rally Monza.